DESCRIPTION (from Application): Osteoporosis is a major public health problem with advanced age. The overall goal of this proposal is to determine whether there are age-related differences in marrow biology that could contribute to the pathophysiology of osteoporosis. We established a novel human cell culture system using bone marrow harvested from discarded femurs at the time of total hip replacement and showed an age-dependence of marrow production of interleukin-6 and generation of osteoclasts. Furthermore, cytochrome P450 aromatase mRNA was found in marrow from both females and males; this suggests that marrow may be a significant peripheral site of estrogen synthesis that could contribute to local regulation of cytokine production and osteoclastogenesis, thereby influencing skeletal metabolism. Marrow biosynthesis of estrogen, aromatase expression, cytokine production, and osteoclastogenesis will be assessed in vitro for at least 240 men and women ranging in age from 25-80 years. Defined groups of postmenopausal osteoporotic and non-osteoporotic women will be characterized for bone mineral density (BMD), body fat, and serum sex steroid levels, and will be controlled for risk factors associated with osteopenia. Relationships between marrow functions and these clinical variables will be defined. SPECIFIC AIM I. We will test the hypothesis that there is an age- dependence of cytokine production and osteoclastogenesis in male and female human marrow. We propose that marrow production of bone active cytokines may stimulate osteoclastogenesis and that endogenous production of sex steroids in marrow may suppress both cytokines and osteoclast differentiation through paracrine mechanisms. We will use a model of human marrow cultured from bones discarded in the course of orthopedic surgery. Further, we will determine the effects of exogenous steroid treatment of cultured marrow on cytokine production and osteoclastogenesis in vitro. This information will increase our understanding of the precise mechanisms by which these hormones may affect bone metabolism in humans. SPECIFIC AIM II. We will test the hypothesis that women with low bone mineral density (BMD) and osteoporosis will show lower estrogen production by marrow and unrestrained cytokine production. We will obtain discarded marrow from osteoporotic and non-osteoporotic women who present for orthopedic surgery. The subjects will be fully characterized with respect to BMD, body fat/lean composition, and steroid levels and other factors associated with skeletal metabolism. We will measure marrow estrogen biosynthesis and aromatase expression in vitro. We will also assess the number of osteoclasts in trabecular bone fragments adjacent to the marrow collected for in vitro analysis. Moreover, we will determine whether these parameters of cytokine production and estrogen synthesis in marrow are related to BMD. The resulting information would represent a major step in understanding the pathogenesis of age related bone loss and why some individuals show greater rates of bone loss and fractures with age.